I have a character called Elias Langley-Black, and right now I know more about his parents than I do about him. Needless to say, this does not make Elias happy. He wants attention, nay, he DEMANDS attention. He demands to be arrogant and unlikable. He demands to have a giant crush on this random Hufflepuff girl called Tomasina Gonzalez (who is also giving me problems, but not as many because she hasn't even got a profile yet). He demands that I give him a backstory and stop obsessing over his half-Indonesian, half-English mother, Enola. He demands--oh, never mind. Elias demands I work on him. Signing off
I seem to be basically the only person in the world without this problem. My characters are all quite well-behaved, really, even the ones that aren't well-behaved in real life.
I think it probably helps that, like in my real life, I don't plan anything, ever. I tend to let my characters have free reign over just about everything, and if one of them changes and doesn't suit a situation, I change the situation. It makes things so much more interesting, having to conform to your characters. The other way around never works